Embed Size (px)
DESCRIPTION
Metamorphic Rocks. Metamorphic Rocks. Key Concept #1. How are metamorphic rocks formed?. extreme heat and/or pressure. Metamorphic Rocks. Key Concept #2. MELTING DOES NOT OCCUR!. If melting occurs, it is classified as an. Igneous Rock. New Minerals Form and Crystals Grow Larger. - PowerPoint PPT Presentation
Citation preview
Metamorphic Rocks
How are metamorphic rocks formed?
MELTING DOES NOT OCCUR!
New Minerals Form and Crystals Grow Larger
Shale Phyllite
SchistGneiss Migmatite
Mud
(Digenesis) Mica/chlorite grains start to align (> 200°C, 3Kbar)
Slate
More chlorite (incl. Biotite), more foliation
Much more mica, and foliation. Porphyroblasts form (andalusite, kyanite and sillimanite, garnet, etc)
More quartz, K-spar, less mica, ~600°C, “compositional layering” starts separating mafic from felsic
700 - 800°C (7.5Kbar) – partial melt, esp. the felsic regions
• Metamorphic Rocks - formed from other rocks, via. heat and pressure (and sometimes fluids)
• Metamorphosis changes the mineral assemblages which are present in a rock
• A Protolith is the original parent-rock from which a metamorphic rock is formed (i.e. limestone is the protolith of marble)
• Occurs @ ~>200°C ~>3 kbars (3000ATM)– Typical geotherm depth = 25°C/Km, so ~8Km std. temp
– 1 kbar per 3 km, so ~9 km depth
What is the difference between
Regional and Contact Metamorphism?
Large geographic area
Example: where mountains form
small geographic area
Example: when rocks come in contact with magma
Key Identifying Features of Metamorphic Rocks
Examples of Foliation…
Slate Phyllite Schist(abundantmicaceousminerals)
Gneiss(fewer
micaceousminerals)
Migmatite
Schistosity Banding Banding
Diagenesis Low grade Intermediategrade
High grade
Increasing intensity of metamorphism
Increasing crystal size
Increasing coarseness of foliation
Low grade Intermediate grade High grade
Dark Red Color
Shiny, flaky
New Minerals Form and Crystals Grow Larger
Shale Phyllite
SchistGneiss Migmatite
Mud
(compaction and
cementation)
Mica/chlorite grains start to align (> 200°C, 3Kbar)
Slate
More chlorite (incl. Biotite), more foliation
Much more mica, and foliation. Porphyroblasts form (andalusite, kyanite and sillimanite, garnet, etc)
More quartz, K-spar, less mica, ~600°C, “compositional layering” starts separating mafic from felsic
700 - 800°C (7.5Kbar) – partial melt, esp. the felsic regions
